This free Plugin for WordPress and ClassicPress allows you to define any of your Pages as 404 Error Page
HTTP error code 404 indicates that the requested page is not found. This is out of your control because you can not do anything about someone else putting a wrong link to your website.
In WordPress and ClassicPress the page that is shown in case of an 404 error is part of the theme. Most of those pages do not provide any information on what to find on your site. Visitors are left in a dead end. The majority of themes do not allow you to customize this page.
That is what the free Plugin 404page for WordPress and ClassicPress is made for. It is the most used plugin to create a custom 404 error page that saves users from being locked in a stalemate which reduces the bounce rate of your site. Just create the page like any other and select that page as your 404 page.
The 404page plugin is designed to work with as many WordPress and ClassicPress themes as possible. If it does not work with your theme you can activate Compatibility Mode, which is able to handle a large part of all compatibility problems.
There are no restrictions. You can create your custom 404 error page completely according to your wishes. Of course you can also use your favorite page builder.